1. Field of the Invention
The invention relates to a film deposition technique using sputtering, and particularly to a technique of handling a substrate after sputtering.
2. Description of the Related Art
Film deposition techniques include vacuum evaporation, sputtering, chemical vapor deposition (CVD), and the like. In a process of manufacturing a semiconductor integrated circuit or the like, sputtering is frequently used to deposit a film for a wiring material and the like.
FIG. 12 is a view illustrating the configuration of an example of a conventional sputtering apparatus. The sputtering apparatus of FIG. 12 mainly comprises: a sputter chamber 1 having a vacuum pump system 11; a cathode 12 and a substrate holder 13 which are disposed so as to oppose each other in the sputter chamber 1; a gas introducing system 14 which introduces a gas into the sputter chamber 1; a sputter power source 15 which applies a given voltage to the cathode 12; a load-lock chamber 2 and an unload-lock chamber 3 which are disposed before and after the sputter chamber 1 through gate valves 22 and 32; a transferring mechanism (not shown) which transfers a substrate 10 in the sequence of the load-lock chamber 2, the sputter chamber 1, and the unload-lock chamber 3. The load-lock chamber 2 has a vacuum pump system 201, and the unload-lock chamber 3 has a vacuum pump system 301.
A number of substrates 10 are housed in a substrate cassette 21 and then placed in the load-lock chamber 2. The load-lock chamber 2 is exhausted to a pressure similar to that of the sputter chamber 1, the gate valve 22 is then opened, and one of the substrates 10 is transferred into the sputter chamber 1 and placed on the substrate holder 13.
After the gate valve 22 is closed, the gas introducing system 14 is operated so as to introduce the gas, and the sputter power source 15 is operated, whereby sputtering is conducted so that a thin film is deposited on the substrate 10. In this case, the substrate 10 is heated to a temperature by heating means 131 disposed in the substrate holder 13. For example, it is known that, when sputtering is conducted in a process of forming a tungsten wiring on an Si foundation while heating the substrate to about 400.degree. C., the resistivity of the tungsten thin film is stabilized at a given value. Consequently, sputtering is conducted while heating the substrate 10 to a temperature of this level.
When the thin film is deposited to a desired thickness, the operations of the gas introducing system 14 and the sputter power source 15 are stopped, and the gate valve 32 is then opened. The transferring mechanism takes out the substrate 10 and the taken-out substrate is housed in a substrate cassette 31 disposed in the unload-lock chamber 3. In this case, also the unload-lock chamber 3 is exhausted to a pressure similar to that of the sputter chamber 1.
In this way, the substrates 10 are transferred one by one from the load-lock chamber 2 into the sputter chamber 1, subjected to sputtering, and then housed in the substrate cassette 31 of the unload-lock chamber 3. When all the substrates 10 which have been housed in the substrate cassette 21 of the load-lock chamber 2 are housed in the substrate cassette 31 of the unload-lock chamber 3 after the film deposition, a vent valve 352 is opened so that a vent gas is introduced into the unload-lock chamber 3, thereby returning the interior of the unload-lock chamber 3 to the atmospheric pressure. Thereafter, the substrates 10 are taken out from the unload-lock chamber 3.
One of the important problems raised in film deposition techniques including sputtering is that the film quality is to be stabilized. In an integrated circuit such as an LSI, particularly, even low-degree degradation of the film quality causes circuit characteristics to be changed, so that the performance of a product is largely affected. In sputtering for a wiring material, for example, the resistivity of a film is required to be stabilized at an expected value.
In the above-described conventional sputtering apparatus, it was ascertained that last several ones of the substrates housed in the substrate cassette of the unload-lock chamber are varied in properties such as the resistivity.
The inventors of the invention have vigorously studied the cause of this phenomenon, and found that the phenomenon is caused by exposing a substrate of a high temperature to the ambient atmospheric pressure. Specifically, with respect to last several ones of the substrates housed in the substrate cassette of the unload-lock chamber, the time period from the timing when the substrates are housed in the substrate cassette to that when the unload-lock chamber is ventilated is short. In other words, these substrates are exposed to the ambient atmospheric pressure after a lapse of a relatively short time period from the timing when the substrates are taken out from the sputter chamber under a high temperature condition. Consequently, it seems that the film of a high temperature captures oxygen, water vapor, and the like contained in the vent gas, and this causes the properties to be varied.